Wax-flux composition containing a succinimide salt of an alkylaryl sulfonic acid for soldering

ABSTRACT

Wax-flux compositions for use in low-temperature soldering processes comprise (A) a major amount of a wax and (B) an effective amount to cause fluxing, at or below the soldering temperature of the piece to be soldered, of a wax-soluble product obtained by first reacting an aliphatic hydrocarbon-substituted succinic acid or derivative thereof which is capable of forming carboximide bonds with an alkylene polyamine to form a carboximide and then reacting said carboximide with an alkylaryl sulfonic acid. A process for soldering electrical components to a printed circuit board comprises (A) applying a molten wax-flux composition as described above to the metal pattern side of the board, (B) allowing the wax-flux composition to solidify, (C) trimming the components leads, and (D) soldering the components to the printed circuit board.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to low-temperature soldering processes. Thisinvention also relates to wax-flux compositions useful in suchlow-temperature soldering processes.

A commercially popular labor saving process for assembling electroniccomponents is to install these components on a printed circuit board.After most, if not all, of the components are installed on the circuitboard, the components are soldered into place by a process known as wavesoldering.

One difficulty with the wave soldering process is that the componentshave leads which extend 1-2 inches beyond the surface of the printedcircuit board. This long length requires a very high standing wave ofsolder. The standing wave can be forced high enough to solder these longlead components but this has disadvantages. Among them, a large amountof solder is lost in coating all these long leads and large globs ofsolder form between groups of leads which extend below the board.However, by soldering the printed circuit board prior to lead trimming,the components are fixed in place and can be trimmed by mechanical meansrather than being hand trimmed, although hand-trimming, of course, isquite feasible.

The disadvantage of trimming a circuit board after it has been solderedis that critical applications, such as military or space applicationsrequire the circuit boards be resoldered subsequent to the trimming.This, of course, greatly increases the expense to the party doing thesoldering as well as increases the risk of damage to the components.

An alternative to soldering the long leads is to hand trim them and bendthe stubs over against the board before soldering. The bent-over stubshold the components in place during the soldering operation. Advantagesof this method are that only one soldering operation is required andonly a low wave of solder need be maintained. The disadvantage is thelarge amount of hand labor required by this method.

What is needed is an inexpensive method which does not involve solder tofix the components in place on the circuit board while the leads arebeing trimmed and which does not interfere with the subsequent solderingoperation.

Wave soldering also uses a flux to clean the printed circuit board andprepare both the component leads and the printed circuit board foil toreceive the solder. In a typical commercial installation, a liquid fluxis maintained in a bath which contains fritted aspirators. Aspiratingthe liquid results in a foam head on the flux tank. The amount ofaspiration is controlled so that the foam head just touches the printedcircuit boards conveyed above it. A light film of the liquid flux isthen deposited on the printed circuit board which subsequently passesover a heater. This preheats the circuit board. The printed circuitboard immediately thereafter passes over the standing wave of solder andthe soldering process is accomplished.

One disadvantage of using this method of applying the soldering flux tothe parts which are to be soldered is that extra equipment is needed. Inaddition, the flux must be aspirated very carefully and constantattention must be paid to the machinery to see that the flux headremains at the right height. If the flux head is too low, obviously theprinted circuit boards will not be properly treated and a poor solderingjob will result. If the flux head is too high, the entire circuit boardincluding the components may be coated with flux which requiresadditional cleaning as well as wastes soldering flux. What is needed isa convenient way to apply the soldering flux to the printed circuitboard which does not require special equipment and special attention.

Certain sulfonic acids, notably the alkylaryl sulfonic acids have beensuggested as suitable fluxing agents for wax-flux compositions. Theseacids are conveniently prepared by oleum sulfonation. However, thisprocess yields sulfonic acids containing a certain amount (often up to2% weight or more) of free sulfuric acid. Sulfonic acid fluxes whichcontain free sulfuric acid tend to stain phenolic printed circuit boardsbrown even at room temperature, but particularly so at elevated (e.g.,soldering) temperatures.

The present invention not only solves the problem of how to firmly fixthe components to the printed circuit board for the lead-trimmingoperation, but also the problem of how to conveniently apply solderingflux to the printed circuit board all in a single-step operation. Thepresent invention also solves the problem of staining of phenolicprinted circuit boards caused by the presence of free sulfuric acid inthe sulfonic acids.

SUMMARY OF THE INVENTION

A wax-flux composition for use in low-temperature soldering processes isprovided comprising (A) a major amount of a wax and (B) an amounteffective to cause fluxing, at or below the soldering temperature of thepiece to be soldered, of a wax-soluble succinimide salt of an alkylarylsulfonic acid. The hardness of the wax at room temperature is chosen toeffectively hold the electronic components in place during an automaticlead-trimming operation. The succinimide salt of an alkylaryl sulfonicacid provides fluxing action during the subsequent soldering stepthereby obviating the need to separately apply a soldering flux. It isbelieved that the salt of the sulfonic acid decomposes at or below thesoldering temperature to provide sulfonic acid which acts as a flux.However, the salt of the sulfuric acid is not so easily thermallydecomposed. Accordingly, the sulfuric acid is not released and thereforedoes not stain the phenolic board.

DETAILED DESCRIPTION OF THE INVENTION

Wax-flux compositions for use in a low-temperature soldering process areprovided comprising: (A) a major amount of a wax having an AmericanMelting Point (AMP determined by ASTM D 127-60) between 40°C and 100°Cand (B) an amount effective to cause fluxing, at or below the solderingtemperature of the piece to be soldered in said process, of awax-soluble product obtained by first reacting a C₂₀ -C₄₀₀ aliphatichydrocarbon-substituted succinic acid or a derivative thereof which iscapable of forming carboximide bonds with a C₂ -C₃₀, N₂ -N₁₀ alkylenepolyamine to form a carboxamide and then reacting said carboxamide witha (C₈ -C₃₀ alkyl)aryl sulfonic acid. In a second embodiment of theinvention a process is provided for soldering electrical components to aprinted circuit board, said board comprising a non-conducting substrateand a pattern of an electrically conductive metal laminated to saidsubstrate, said metal being solderable with a low-melting-point alloysolder, said board having component lead receiving holes through bothsaid substrate and said metal pattern, comprising:

a. applying a molten wax-flux composition described above to the metalpattern side of said board and to said component leads;

b. allowing said wax-flux composition to solidify;

c. trimming said component leads; and

d. soldering said component to said printed circuit board with alow-melting-point alloy solder.

The Wax

Suitable waxes for use in the wax-flux compositions of this inventionand in the soldering processes of this invention include any wax or waxblend which is solid at room temperature and has a melting point belowthe temperature at which the soldering process will be conducted.Preferably the waxes have an AMP of at least 40°C and generally thewaxes will have an AMP not greater than 100°C. Preferably the waxes havean AMP between 50°C and 80°C.

Suitable waxes include petroleum-derived waxes such as the well knownparaffin waxes. These paraffin waxes are obtained from the processing ofcrude petroleum and are generally substantially saturated, substantiallystraight long-chain aliphatic hydrocarbons. Petroleum waxes suitable foruse in this invention have AMP's within the range specified above.

Suitable wax blends for use in this invention include the hot meltcoatings which consist of blends of petroleum waxes and polymers,copolymers or resins. Suitable materials which may be blended with thepetroleum waxes include polymers of low molecular weight olefins, suchas polymers of ethylene, propylene, butylene, isobutylene, and the like.Suitable polymers will have molecular weights from about 1000 to about1,000,000, more usually from about 1000 to about 50,000. These areaverage molecular weights and generally a major portion of the moleculesof the polymer will have molecular weights close to the average.

Suitable copolymers include copolymers of olefins with olefinic esterssuch as ethylene-vinyl acetate copolymers. These copolymers arecommercially available from E. I. DuPont DeNemours & Company under thetrade name ELVAX. Other suitable copolymers include copolyers ofdifferent olefins such as the copolymers of propene and butene.Typically such a copolymer will contain from about 15 to about 85 molpercent propene, more usually from about 25 to 75 mol percent propene.Typical copolymer molecular weights will range from about 1000 to about1,000,000, more usually from about 1000 to about 300,000.

Other suitable wax blends include wax compositions incorporatingcellulose esters or cellulose ethers. Suitable cellulose esters includealkyl esters of cellulose wherein the cellulose molecule contains, onthe average, 3 alkyl radicals per glucose unit, i.e., the celluloseesters are triesters of cellulose. Typically, the alkyl radicals containfrom about 7 to about 16 carbon atoms which include cellulosetriheptanoate, cellulose trioctanoate, cellulose tridecanoate, cellulosetrilaurate, etc.

Suitable cellulose ethers include the di- and triethers of cellulosewherein the ether radicals are hydrocarbon radicals, preferably alkylradicals each having from 1 to 18 carbon atoms, with the combined totalnumber of carbon atoms preferably being at least 12. In other words,although each of the hydrocarbon ether radicals on each glucose unit ofthe cellulose has from 1 to 18 carbon atoms, the total number of carbonatoms preferably is at least 12. In the case of diethers, one of theether radicals preferably contains at least 8 carbon atoms. Suitableethers of cellulose include cellulose methyl octyl ether, celluloseethyl octyl ether, cellulose ethyl decyl ether, cellulose ethyl dodecylether, cellulose ethyl tetradecyl ether, cellulose propyl octyl ether,cellulose butyl octyl decyl ether, cellulose methyl butyl amyl ether,cellulose tri(butyl) ether, cellulose methyl octyl octadecyl ether, etc.

Typically the cellulose, prior to etherification or esterification, hasa molecular weight ranging from about 40,000 to about 500,000. Typicallythe cellulose esters and cellulose ethers are used in the waxcompositions in amounts ranging from about 2 to about 30 percent,preferably from about 10 to about 20 percent by weight.

Suitable waxes for this invention also include waxes obtained fromnatural sources, such as animal, vegetable or insect sources. Suitablewaxes include beeswax, carnuba wax, montan wax, wool wax, and the like.

Another type of wax suitable for use in this invention includes the wellknown Fischer-Tropsch waxes. Fischer-Tropsch waxes are waxes synthesizedby the familiar Fischer-Tropsch process. By this process, coal is burnedin the presence of oxygen and steam to produce hydrogen and carbonmonoxide, which are then reacted in the presence of catalyst to make thedesired hydrocarbon wax. Suitable Fischer-Tropsch waxes for thisinvention can be obtained under the trade name "Paraflint". Theseparticular Fischer-Tropsch waxes have a high molecular weight, on theaverage in the range of about 750 to 1000 and generally consistessentially of straight-chained hydrocarbons.

Although the above waxes have been mentioned individually suitable waxesfor this invention include mixtures of various proportions of theabove-mentioned waxes.

The Fluxing Agent

The wax-flux compositions provided by this invention and useful in theprocess of this invention include a wax-soluble succinimide salt of analkylaryl sulfonic acid. Such fluxing agents are obtained by firstreacting an aliphatic hydrocarbon-substituted succinic acid orderivative thereof which is capable of forming carboximide bonds with analkylene polyamine to form a carboximide and then reacting saidcarboximide with an alkylaryl sulfonic acid.

In preparing the first reaction product, the aliphatichydrocarbon-substituted succinic acid will normally be used as ananhydride, although other acid derivatives which are capable of formingcarboximide bonds may be employed. The reaction will be carried out sothat least one imide is formed. The alkylene polyamine which is employedwill have at least 2 carbon atoms and at least 2 nitrogen atoms, thenitrogen atoms being separated by at least 2 carbon atoms. Normally thealkylene polyamine will not be of more than 10 nitrogen atoms and notmore than 30 carbon atoms.

The polyamine and succinic acid compounds are combined in a mol ratio ofat least 0.1:1 to about 1.5:1, more usually from about 0.1:1 to about1.2:1. The conditions of reaction are such that as imide formation isobtained, the water of reaction is removed. While mixtures are obtained,the reaction product will normally be an imide with other minor productsalso present such as amides, imidazolines, amine salts, etc. There willbe at least one full equivalent of amine nitrogen in excess over thenumber of mols of succinic compound, and preferably at least 2equivalents in excess. That is, at least one basic amine nitrogen willbe present per molecule, so that the basic amine nitrogen is availableto form a salt with the alkylaryl sulfonic acid.

The first reaction product and the alkylaryl sulfonic acid are thencombined to form a salt. The most important consideration in determiningthe quantity of the first reaction product to be combined with thesulfonic acid is to be certain there are sufficient titratable aminenitrogens present in the first reaction product to react with all of thesulfuric acid present in the sulfonic acid. Typically, however, thequantity of the first reaction product used is more than the minimum.Generally, the alkylaryl sulfonic acid is employed in an amount of from1 mol per mol of first reaction product up to about 2 mols of sulfonicacid per basic titratable amine nitrogen atom in the first reactionproduct.

The succinic compound, usually the succinic anhydride, will be combinedwith the polyamine at a temperature in the range of about 90°-275°C,more usually about 100°-200°C. The time for the reaction will generallybe from about 1/2 hour to 24 hours, more usually in the range of about 1to about 12 hours, and preferably in the range of about 3 to about 7hours.

Conveniently the reactants may be combined in an inert reaction mediumsuch as a hydrocarbon, e.g., mineral lubricating oil. The concentrationof reactants may range from about 1 to about 90% weight, but usuallywill be from about 25 to about 75% weight of the total reaction mixture.Preferably the water formed during the reaction is removed either bydistillation or, if convenient, subatmospheric pressures may beemployed.

The sulfonic acid salt may then be prepared directly by adding thealkylaryl sulfonic acid either at room temperature or at elevatedtemperatures to the first reaction product to form the desired salt. Thereaction may be carried out neat or in an inert medium such as thatemployed in preparing the first reaction product.

The wax-soluble product useful in the compositions of this invention,for the most part, will be comprised of a product of the formula##EQU1## wherein X represents ##EQU2## and wherein:

A. R¹ and R⁴ each independently represent hydrogen or an alkylcontaining from 1 to about 5 carbon atoms such as methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, amyl, t-amyl,and the like;

B. A is an alkylene radical containing from 2 to about 6 carbon atomssuch as ethylene, propylene, trimethylene, tetramethylene,pentamethylene, hexamethylene, and the like;

C. y is a number from 0 to 10;

D. such that when A represents ethylene, the R¹ groups on adjacentnitrogen atoms may be joined to form ethylene;

E. R³ represents an alkyl or alkenyl radical of from about 20 to about400 carbon atoms such as long-chain hydrocarbons or polymers andcopolymers of low-molecular-weight olefins such as ethylene(copolymerized with olefin containing more than 2 carbon atoms),propylene, butylene, isobutylene, and the like;

F. Ar represents an aryl group such as phenylene, naphthalene,anthracenylene, and the like, preferably phenylene;

G. R² represents a wax-solublizing group containing 1 to about 22 carbonatoms, such as methyl, ethyl, propyl, butyl, isobutyl, t-butyl, pentyl,hexyl, octyl, tripropenyl, decyl, dodecyl, tetrapropenyl, tridecyl,tetradecyl, pentadecyl, pentapropenyl, hexadecyl, octadecyl,hexapropenyl, eicosyl, docosyl, and the like;

H. n represents a positive integer of from 1 to 3;

I. such that the total number of carbon atoms contained in all of saidR² groups is from about 8 to about 30 carbon atoms; and

J. z represents a number from 1 up to about twice the number oftitratable amine nitrogens, preferably z represents a number such thatthe ratio of z to the number of titratable nitrogen atoms is from about0.9 to about 2.1.

The above formula is intended to represent symbolically the number ofatoms present in the molecule, but not to represent the actual structureof the molecule. Thus, the alkylene and alkylene piperazine componentsneed not be present in any particular order but may be interspersedamong one another. Similarly, the alkylaryl sulfonic acid portion of themolecule in the above formula is intended to include ionic structures.

The aliphatic radical substituent R³ is readily obtained by polymerizingmonoolefins of from 2 to 5 carbon atoms, such as ethylene (copolymerizedwith olefins containing more than 2 carbon atoms), propylene, n-butene,isobutylene, or pentene, or mixtures thereof. Methods of polymerizationare well known in the art, as are methods of substituting the aliphaticchain onto the succinic anhydride structure.

The polyamine with which the aliphatic hydrocarbon-substituted succinicanhydride is reacted contains 2 to 30 carbon atoms, 1 to 10 nitrogenatoms, and preferably 1 to 6 nitrogen atoms as its only hetero atoms. Itis free of unsaturation. The nitrogen atoms in the secondary aminogroups are joined by alkylene or piperazine groups of from 2 to 6 carbonatoms and, more usually, of from 2 to 3 carbon atoms. These nitrogenatoms may be substituted with hydrogen or lower alkyl of 1 to 6 carbonatoms, preferably of from 1 to 3 carbon atoms.

The polyamine reactant preferably has the following formula: ##EQU3##wherein A, R¹, R⁴, and y have the meanings set forth above, such thatthe R⁴ groups on at least one of the terminal nitrogen atoms bothrepresent hydrogen. Illustrative alkylene polyamines and polyalkylenepolyamines of the foregoing types include ethylene diamine, diethylenetriamine, triethylene tetraamine, tetraethylene pentamine, pentaethylenehexaamine, nonaethylene decamine, dipropylene diamine, dimethylaminopropylamine, N-amino ethyl piperazine, and the like.

The hydrocarbon sulfonic acids have the general formula:

    (R.sup.2).sub.n Ar-SO.sub.3 H

wherein R², Ar, and n have the same meanings as set forth above. Thesesulfonic acids can be obtained from a variety of sources, both naturaland synthetic. Sulfonic acids can be derived from petroleum products bytreating such products with sulfuric acid or sulfur trioxide. Thecompounds in the petroleum product which become sulfonated contain awax-solubilized group, as discussed above. The acids thus obtained areknown as petroleum sulfonic acids. Also included are sulfonic acids ofsynthetic alkylaryl compounds. These acids are prepared by treating analkylaryl compound with sulfuric acid or sulfur trioxide. At least onealkyl substituent of the aryl compound is a was-solubilized group, asdiscussed above. The acids thus obtained are known as alkyl arylsulfonic acids. These sulfonic acids whrein the alkyl is astraight-chain alkyl are the well-known linear alkyl sulfonic acids(LAS). A number of synthetic sulfonic acids are available. Aparticularly useful synthetic sulfonic acid is available under the nameCal Soft LAS 99, available from Pilot Chemical Company. This sulfonicacid is primarily a linear C₁₂ alkyl-benzene sulfonic acid. Anotheruseful synthetic sulfonic acid is dodecyl benzene sulfonic acid,available from Chemithon Chemical Co.

Most of the commercially available sulfonic acids contain small amounts(generally less than 2% by weight) of free sulfuric acid remaining inthe sulfonic acid from the sulfonation step. This sulfonic acid cancause a staining problem with phenolic circuit boards, as mentionedabove. By combining the sulfonic acid with the succinimide, as providedin this invention, the succinimide not only chemically ties up thesulfuric acid in such a manner that it no longer stains the phenolicboards, but the succinimide also provides some additional fluxing actionover and above that obtained with the sulfonic acid. In addition, thesuccinimide portion of the salt imparts dispersing properties to thecomposition, which helps disperse any impurities or sludge formed duringmanufacture or use throughout the composition.

In the preparation of the wax-soluble products mentioned above, if asolvent is used, it is generally removed after the reaction is completeso as to not impart any undesired properties to the wax-fluxcompositions prepared therefrom. Such undesirable properties wouldinclude fuming of the wax-flux composition when it is melted forapplication to the circuit board.

The Wax-Flux Compositions

The wax-flux compositions of this invention are prepared by melting thewax or wax blend and dissolving the succinimide salt therein. Themixture is then stirred until homogeneity is obtained. The wax-fluxcomposition is cast into blocks or slabs and allowed to solidify unlessit is to be immediately used.

The wax-flux compositions of this invention will contain an amounteffective to cause fluxing, at or below the soldering temperature of thepiece to be soldered, of the wax-soluble succinimide salt. Thiseffective amount can readily be determined by those skilled in the artby a few simple soldering tests to determine the minimum amountnecessary. Any amount above the minimum necessary to cause effectivefluxing generally is not necessary and increases the cost of thewax-flux composition without additional benefits during the solderingprocess. Typically, the wax-flux compositions will contain from about 1to about 20 weight percent of the succinimide salt, more usually fromabout 3 to about 12 weight percent and preferably from about 5 to about10 weight percent.

The Process

The wax-flux compositions of this invention are useful in the solderingprocess of this invention. The soldering process for this inventionprovides a method for soldering electrical components to a printedcircuit board. Printed circuit boards are well known in the art. Theyconsist of a non-conducting substrate and a pattern of an electricallyconductive metal laminated to the substrate. Typically, the substrate isa phenolic resin or an epoxy fiberglass composition board. Almostuniversally the electrically conductive metal is a copper foil. Thepattern of the conductive metal on the substrate can be prepared by anumber of means well known to those skilled in the art.

The printed circuit board has lead receiving holes. The electricalcomponent leads are inserted through the holes from the non-pattern sideof the board. Typically, the electrical components have leads whichextend 1 to 2 inches beyond the pattern side of the board. In some priorart methods of soldering the components to the board, the leads aresoldered to the metal pattern and then the lead is trimmed relativelyclose to the board.

The process of this invention is particularly applicable to automatedsoldering with wave soldering machines. Wave soldering machines arecommercially available from a number of sources and are used by most ofthe electronics industry manufacturers. As mentioned above, aparticularly troublesome problem in trying to solder electroniccomponents to printed circuit boards with wave soldering machines is thelong leads of the electronic components which extend beyond the board.

In the process of this invention, the component leads are insertedthrough the holes of the printed circuit board. Then without trimmingthe leads, the molten wax-flux composition is applied to the metalpattern side of the circuit board and allowed to solidify. Once thewax-flux composition has solidified, the components are firmly attachedto the board and the component leads can be trimmed prior to thesoldering operation.

The component leads of the waxed board can be trimmed by any availablemethod including hand-trimming and automated trimming. A most convenientmethod of trimming uses a high-speed circular metal-cutting saw. Oneexample of such a saw is a 16-inch high-speed circular saw sold byHollis Engineering Company of Nasha, New Hampshire under the nameHolli-Cutter. To use the Holli-Cutter, the printed circuit board isplaced on a conveyer which passes over the circular saw. The spacebetween the printed circuit board and the saw blade is adjusted to givetrimmed leads of the desired length.

After the leads are trimmed, the electrical components are soldered tothe printed circuit board with a low-melting-point alloy solder. Thissoldering operation can be conducted by any of the conventionallyavailable means such as by hand-soldering or by automated wavesoldering.

In a preferred embodiment of the process, the wax-flux composition isapplied to the printed circuit board by contacting the metal patternside of the board with the crest of a standing wave of molten wax-fluxcomposition. Thereafter the wax-flux composition is allowed to solidify,generally with the aid of a forced draft of cold air. The componentleads are then trimmed by an automated cutting means which is placed inline with the conveyer carrying the printed circuit board. Thereafterthe components are soldered to the board by contacting the metal patternside of the board with the crest of a standing wave of thelow-melting-point alloy solder, typically, in one of the commerciallyavailable automated wave soldering machines.

When a wave soldering machine is used, it is often found advantageous tomaintain a thin film of tinning oil over the surface of the standingpool of molten solder in the catch basin of the wave soldering machine.The tinning oil helps reduce oxidation and dross formation of the moltensolder which can lead to poor soldering. Suitable tinning oils areavailable commercially. One such tinning oil is available from HollisEngineering Company and comprises a bright stock containing fats, fattyacids, naturally occurring unsaturated long-chain acids, and oxidationinhibitors.

Typically, the tinning oil is changed approximately every 8 hours. Inthe process of this invention, the tinning oil becomes contaminated withthe wax-flux composition which melts and is removed from the printedcircuit board during the soldering operation. It has been found such asmall quantity of wax-flux composition is coated onto each board, thateven with a very high soldering rate, the wax-flux compositioncontamination of the tinning oil does not cause a significant reductionin the useful life of the oil. This slight increase in the frequency ofchanging the tinning oil is a very small price to pay for theconvenience and improved soldering offered by the process of thisinvention.

Subsequent to the soldering process, any remaining traces of the fluxare generally removed from the printed circuit board. This preventspotential long-term corrosion of the printed circuit board and thecomponent leads.

The flux and tinning oil can be removed either by vapor degreasing oraqueous washing. Machines are available commercially for practicing bothmethods. For aqueous washing, these generally resemble largedishwashers. Typically, the wash water is maintained between 60°C and72°C. Generally a detergent is used during the washing process. Typicaldetergents are mixtures of alkaline surface-active agents and nonionicsurface active agents. Suitable commercially available detergentsinclude Aqua-Clean available from Hollis Engineering Company andLonco-Terge available from Lonco Corporation.

As a final step of the washing process the circuit boards are rinsedwith warm or hot deionized or distilled water to remove the last tracesof the fluxing agent and the detergents.

EXAMPLES

The following examples are included to further illustrate preparation ofthe succinimide salts of the alkylaryl sulfonic acids useful in thewax-flux compositions of this invention.

Example 1

To a beaker is charged 31.8 g of a polyisobutenyl succinimide producedby reacting a polybutene (having a number average molecular weight of950) substituted succinic anhydride with tetraethylene pentamine at anamine/anhydride mol ratio of 0.87 as a 44% weight solution in a neutralsolvent-refined oil and 9.8 g of dodecyl benzene sulfonic acidcommercially available as Cal-Soft LAS 99 (sulfonic acid -- minimum 97%weight, sulfuric acid -- maximum 1.5% weight). Thesuccinimide-to-sulfonic acid mol ratio is 1:3. The calculated molecularweight for the succinimide is determined by dividing the nitrogencontent of the succinimide into 70, the sum of the atomic weight of the5 nitrogen atoms present in the ideal succinimide molecule prepared fromtetraethylene pentamine, which in this case yields a calculatedmolecular weight of 3300. The molecular weight of the sulfonic acid wastaken as the theoretical molecular weight of 326 for dodecyl benzenesulfonic acid. This mixture is stirred at 137.5°-143.5°C for 3 hours.The oil solution of the product is designated as I-A.

In a similar manner, 31.8 g of the same succinimide and 16.3 g of thesame sulfonic acid are stirred at 137.5°-143.5°C for 3 hours. Thesuccinimide-to-sulfonic acid mol ratio is 1:5. The oil solution of theproduct is designated as I-B.

In a similar manner, 31.8 g of the same succinimide and 22.8 g of thesame sulfonic acid are stirred at 137.5°-143.5°C for 3 hours. The molratio of the succinimide to sulfonic acid is 1:7. The oil solution ofthe product obtained is designated as I-C.

In all of the above reactions, evolution of the heat of salt formationwas observed.

Example 2

Succinimide salts are prepared in a similar manner as that used inExample 1 above using the same succinimide but using a dodecyl benzenesulfonic acid available from Chemithon Chemical Company, having ananalysis of 0.4% weight sulfuric acid, 8.1% weight of diluent oil and90.5% weight of dodecyl benzene sulfonic acid.

In a first reaction at a succinimide-to-sulfonic acid mol ratio of 1:5,31.8 g of the succinimide and 18 g of the sulfonic acid are stirred at137.5°-143.5°C for 3 hours. Evolution of the heat of salt formation wasobserved. The oil solution of this product is designated as II-A.

In a similar manner, at a succinimide-to-sulfonic acid mol ratio of 1:7,31.8 g of the same succinimide and 25.2 g of the sulfonic acid areheated with stirring for 3 hours. Evolution of the heat of saltformation was observed. The oil solution of this product is designatedas II-B.

Example 3

A bis-succinimide is prepared by reacting a polybutene (averagemolecular weight 950) substituted succinic anhydride with tetraethylenepentamine at an amine/anhydride mol ratio of 0.5. The bis-succinimide isused as an approximately 40% solution in a diluent oil.

In a beaker, 48.7 g of the bis-succinimide and 16.3 g of the Cal-SoftLAS 99 sulfonic acid are heated with stirring at 137.5°-143.5°C for 3hours. The bis-succinimide/sulfonic acid mol ratio is 1:5. The oilsolution of this product is designated as III-A.

In a similar manner, at a bis-succinimide/sulfonic acid mol ratio of1:7, 48.7 g of the bis-succinimide and 22.8 g of the sulfonic acid areheated with stirring for 3 hours. The oil solution of this product isdesignated as III-B.

In a similar manner, at a bis-succinimide/sulfonic acid mol ratio of1:3, 48.7 g of the bis-succinimide and 9.8 g of the sulfonic acid areheated with stirring for 3 hours. The oil solution of this product isdesignated as III-C.

Each of the above examples 1-3 is repeated with the only change inprocedure being that the reaction mixture is heated with stirring at theindicated temperature for 5 hours rather than for 3 hours.

The following examples are included to further illustrate soldering withthe wax-flux compositions of the invention.

Wax-flux compositions of this invention are tested in commerciallyavailable wave soldering equipment. The results of these tests arecompared against soldering operations conducted in commerciallyavailable wave soldering equipment using a commercially available wavesoldering flux, namely Alpha Reliafoam 809 Flux available from AlphaMetals, Inc., 56 Water Street, Jersey City, New Jersey 07304. This fluxis one of the most widely used commercially available liquid fluxes forwave soldering. It has been found to have the capacity to satisfactorilyflux copper printed circuit boards having visible dirt, tarnish andcorrosion.

For soldering sample printed circuit boards using the commerciallyavailable Alpha flux, the wave soldering equipment comprises an in-lineunit having a foam flux applicator, a preheater, an a wave solderapplicator. The in-line unit includes a conveyer which transports theboards through the various steps of the soldering operation. Printedcircuit boards for the soldering operation are prepared by inserting theleads of electronic components through the holes in the printed circuitboard, trimming the leads, and bending the stubs over against the copperfoil. The printed circuit boards used in these tests are deliberatelyprepared to be dirty, tarnished and difficult to solder.

For soldering printed circuit boards using the wax-flux composition ofthis invention the wave soldering equipment includes a wax-fluxapplicator in which the molten wax-flux composition at about 75°-95°C ispumped into a standing wave about 4-5 cm in height. Next in line is alead trimmer which is, in this case, a Holli-Cutter available fromHollis Engineering, Inc. The Holli-Cutter comprises a 16-inch high-speedtungsten carbide-tipped circular saw. After the lead trimmer is theboard preheater and then the wave solder applicator. The leads ofelectronic components are inserted through the holes in the printedcircuit board. The leads are left untrimmed. The board with theelectronic components is placed on the conveyer of the solderingapparatus. The printed circuit board is conveyed first over the wax-fluxwave. A thin film of wax-flux remains on the underside of the printedcircuit board. The board then passes over a forced draft of cool airwhich cools and solidifies the wax. The board then passes over the leadtrimmer and the electronic component leads are trimmed to the desiredlength. The board then passes over the flux preheater and over the waveof solder. The printed circuit boards soldered with the wax-fluxcomposition of this invention and according to the process of thisinvention are then compared with the printed circuit boards solderedusing the commercially available liquid flux.

Example 4

Each of the succinimide salts of the sulfonic acids prepared in Examples1-3 above are blended with a refined base wax having an AMP of 154-156,such that the wax blend contains 10% weight of the oil solution of theproduct. Each of these wax-flux blends is tested on a Meniscograph andfound to exhibit a satisfactory time to wet and total wetting of thecopper coupon in a soldering operation.

Example 5

A wax-flux composition comprising 90% weight refined base wax having anAMP of 154-156 and 10% weight of an oil solution of a succinimide saltof Cal-Soft LAS 99 is tested in a wave-soldering apparatus.

The succinimide salt is prepared by combining 12,000 g of a 44% weightsolution of the succinimide used in Example 1 above with 6000 g ofCal-Soft LAS 99. This mixture was heated with stirring at 137°-138°C for4 hours.

The wax-flux composition securely attaches the electronic components tothe printed circuit board and allows fully satisfactory automated leadtrimming. During the soldering step, this wax-flux composition providesfluxing and allows powdering comparable to the commercially availablesoldering flux.

Subsequent to the soldering step, the printed circuit board is washed ina circuit board washer using 71°C aqueous detergent solution containingHollis Aqua-Clean. The washed boards are completely clean and free fromany wax or oil residue.

What is claimed is:
 1. A wax-flux composition for use in alow-temperature soldering process, comprising:A. a major amount of a waxhaving an AMP between 40°C and 100°C; and B. an amount effective tocause fluxing, at or below the soldering temperatures, of the piece tobe soldered in said process of a wax-soluble product obtained by firstreacting a C₂₀ -C₄₀₀ aliphatic hydrocarbon-substituted succinic acid ora derivative thereof which is capable of forming carboximide bonds witha C₂ -C₃₀, N₂ -N₁₀ alkylene polyamine to form a carboximide and thenreacting said carboximide with a (C₈ -C₃₀ alkyl)aryl sulfonic acid. 2.The wax-flux composition of claim 1 wherein said product is derived froman aliphatic hydrocarbon-substituted succinic anhydride.
 3. The wax-fluxcomposition of claim 2 wherein said wax-soluble product has the formula##EQU4## wherein X represents: ##EQU5## with at least one X being thelatter radical; R¹ and R⁴ each independently represent hydrogen or analkyl containing from 1 to about 5 carbon atoms; A is an alkyleneradical containing from 2 to about 6 carbon atoms; y is a number from 0to 10 such that when A represents ethylene R¹ on adjacent nitrogen atomsmay be joined to form ethylene; R³ represents an alkyl or alkenylradical of from about 20 to about 400 carbon atoms; Ar represents anaryl group; R² represents a wax-solubilizing group containing from 1 toabout 22 carbon atoms; n represents a positive integer of from 1 to 3wherein the total number of carbon atoms contained in all of said R²groups is from 8 to about 80 carbon atoms; and z represents a numberfrom 1 up to the number of titratable amine nitrogens.
 4. A wax-fluxcomposition of claim 3 wherein Ar represents phenylene or naphthalene.5. A wax-flux composition of claim 3 wherein R⁴ represents hydrogen; R³is a branched-chain aliphatic radical of from 50 to 200 carbon atoms; Arepresents alkylene of from 2 to 3 carbon atoms; y represents a positiveinteger from 0 to 5 when one X is --NH₂ and 1 to 5 when neither X is--NH₂ ; and z represents a number such that the ratio of z to the numberof titratable nitrogen atoms is from about 0.9 to about 2.1.
 6. Awax-flux composition of claim 5 wherein said wax-soluble productcomprises 1 to 20 weight percent of said composition.
 7. A wax-fluxcomposition of claim 5 wherein said wax-soluble product comprises fromabout 3 to about 12 weight percent of said composition.
 8. A wax-fluxcomposition of claim 6 wherein Ar represents phenylene, R² represents analkyl containing from 8 to 22 carbon atoms and n equals
 1. 9. A wax-fluxcomposition of claim 8 wherein R² represents dodecyl.
 10. A wax-fluxcomposition of claim 9 wherein said wax has an AMP of from 50°C to 75°C.11. A wax-flux composition of claim 8 wherein R² representstetrapropylene.
 12. A wax-flux composition of claim 11 wherein said waxhas an AMP of 50°C to 75°C.